The general structure of a turbojet engine shall now be mentioned in brief with reference to FIG. 1. The turbojet engine is traversed by a current of axial air (symbolized by the arrow F). It successively includes a blower or low-pressure compressor 1, a high-pressure compressor 3, a combustion chamber 5, a turbine 7 and an air ejection pipe 9. The air sucked up by the turbojet engine successively traverses the low-pressure compressor 1 and the high-pressure compressor 3 where it is compressed, and then the combustion chamber where it is heated, and finally the pipes 9 where it is ejected.
The constant search for weight reduction has led motorization technicians to study and produce compressors fitted with hollow vanes or vanes made of a composite material. The use of these techniques unfortunately results in the production of vanes which are more fragile than those vanes used hitherto.
Furthermore, increasing of the diameter of blowers is a determinant factor concerning the risks of foreign bodies being sucked up from the ground or during flight. For example, these foreign bodies may be birds which may be present in large numbers when airplanes fly at high speeds or at low altitudes. At high altitudes, these foreign bodies may be pieces of ice.
When these foreign bodies penetrate into the blower or low-pressure compressor 1, they generally result in a slight movement in the axial direction of the vanes of the stator or the vanes of the rotor, and indeed may even result in breaking of these vanes as they are quite fragile. When a vane of a stage moves, they abut against the vanes of the next stage and thus break. The vane fragments then penetrate into the high-pressure compressor 3 resulting in secondary damage to the vanes of the stator and the rotor.
It is thus important to ensure that the vanes do not move axially towards the front or rear of the turbojet engine as a result of an impact with a foreign body.
One first solution to try to resolve the damage caused to vanes by foreign bodies entering is described in the patent application FR-2 326 603. The vane described in this document is intended to be placed in an air flow blowing channel and be disposed in series with an adjacent vane against which it is likely to abut in the event of an impact occurring. These vanes are conventionally orientated radially inside the blowing channel. Each vane is constituted in this case by one metallic main portion fitted at its extremities with pivots allowing for a selective rotation of the vane around the axis defined between the two pivots. This vane has in its external downstream radial portion a block made of a composite material. This block is generally made of a graphite-epoxy composite material and forms the trailing edge of the vane. It is fixed rigidly to the rest of the vane by means of an adhesive, for example. This block is able to break and separate from the metallic portion, either when it directly receives an impact, or when the vane moves and when the block abuts against the following vane. Thus, at the time of impact, only the more fragile block made of a composite material is split into small pieces and, when these pieces are sucked up by the compressor, they do not cause any secondary damage downstream.
This technique, even if it does partially limit damage caused to the vanes of the secondary stages of the compressor, does not prevent the axial movement of this vane.
The vanes of the prior art are generally fixed as shown on FIG. 2.
The vane 11 is fixed at its two extremities between an external casing of the cylindrical stator (not shown in FIG. 2) and an internal ring-shaped ferrule 13 disposed coaxially inside the external casing. Each vane 11 has at its internal radial extremity a platform 14 ending in a pivot 15. This pivot 15 is maintained between two annular half-rings 17 and 19 fixed around the ferrule 13 of the compressor. An antifriction washer 20 is placed between the pivot 15 and the two half-rings 17 and 19. In addition, these two half-rings 17 and 19 are kept assembled by a set of soldered plates 21 which comprise a gasket 22. As can be seen in FIG. 2, the vane 11 is not locked at its base (towards the center of the engine), and the platform 14 merely rests inside a housing 23 provided in the half-rings 17 and 19. This explains the easy axial movement of the vane when a foreign body enters.